DC to DC converters are important in portable electronic devices such as cellular phones and laptop computers and are supplied with power from batteries. Such electronic devices often contain several sub-circuits each with its own voltage level requirement different from that supplied by the battery or an external supply (sometimes higher or lower than the supply voltage). A battery's voltage, for example, declines as its stored power is drained. Switched DC to DC converters offer a method to increase voltage from a partially lowered battery voltage thereby saving space instead of using multiple batteries to accomplish the same thing.
Electronic switch-mode DC to DC converters transform one DC voltage level to another, by storing the input energy temporarily and then releasing that energy to the output at a different voltage. The storage may be in either magnetic field storage components (inductors, transformers) or electric field storage components (capacitors).
FIG. 1 illustrates a block diagram of a conventional DC-DC converter 100.
As illustrated in the figure, DC-DC converter 100 contains a controller 102, a power source 104, a power stage 106, a power stage 108, and a load 110.
Controller 102 is in communication with power stage 106 via a line 112 and is in communication with power stage 108 via as line 114. Power source 104 is in communication with power stage 106 and power stage 108 via a line 116. Power stage 106 and power stage 108 are in communication with controller 102 and load 110 via a line 118.
Controller 102 controls power stage 106 with a control signal 120, via line 112, and controls power stage 108 with a control signal 122, via line 114. Power source 104 delivers a DC current 124 to power stage 106 and power stage 108, via line 116.
Power stage 106 generates a power signal 126, based on control signal 120. Power signal 126 has an associated voltage and current. For purposes of discussion, let the maximum voltage generated by power stage 106 be a constant voltage, whereas the current generated by power stage 106 may be varied in response to control signal 120 so as to vary the resultant power signal 126. In this manner, when power signal 126 changes, it changes based on a change in the associated current.
Power stage 108 generates a power signal 128, based on control signal 122. Power signal 128 has an associated voltage and current. For purposes of discussion, let the maximum voltage that may be generated by power stage 108 be a constant voltage that is, at most, equal to the voltage generated by power stage 106, whereas the current generated by power stage 108 may be varied in response to control signal 122 so as to vary the resultant power signal 128. In this manner, when power signal 128 changes, it changes based on a change in the associated current.
Power signal 126 adds to power signal 128 to make load power 130, which is provided to load 110 and to controller 102. For purposes of discussion, let each of power stage 106 and power stage 108 be able to deliver a maximum current of 1.0 A at 3.0 V to load 110. For example, let power stage 106 and power stage 108 provide, ideally, a fixed voltage via an output inductor (not shown). However, as the impedance of an inductor is based on the frequency of the alternating current conducted there through, the actual output voltage may vary.
The operation of DC-DC converter 100 will now be discussed with additional reference to FIGS. 2A-C.
FIG. 2A illustrates load power 130 DC-DC converter 100.
The figure includes a graph 202 and a graph 204. Graph 202 includes a Y-axis 206, an X-axis 208, a current function 210 and a current function 212. Graph 204 includes a Y-axis 214, X-axis 208 and a voltage function 216.
Graph 202 represents the current of load power 130 over time in DC-DC converter 100, whereas graph 204 of load power 130 represents the voltage over time in DC-DC converter 100. Y-axis 206 represents current in Amperes, whereas Y-axis 214 represents voltage in Volts. X-axis 206 represents time in ms.
Current function 210 corresponds to power signal 126 of power stage 106, as shown in FIG. 1, over time. Current function 212 corresponds to power signal 128 of power stage 108, as shown in FIG. 1, over time. In this example, power signal 128 is zero, so power signal 126 is equal to load power 130, as shown in FIG. 1. As such, in this example current function 210 additionally corresponds to load power 130 over time. Current functions 210 and 212 are each illustrated as a direct current (DC) to simplify the discussion. In should be noted that each function may be additionally described with an alternating current (AC).
Voltage function 210 corresponds to a voltage associated with load power 130, as shown in FIG. 1, over time.
In FIG. 2A, as shown by current function 210, power stage 106 is outputting power signal 126 at 1.0 A. Simultaneously, as shown by current function 212, power stage 108 is not outputting any current. When only power stage 106 is outputting current 116 to load 110, DC-DC converter 100 is in single phase mode.
Returning to FIG. 1, in operation, controller 102 determines the voltage and current to be provided to load 110. In this non-limiting example, controller 102 determines 1.0 A of single phase current at 3.0 V should be generated.
Controller 102 compares the determined current to be provided to load 110 with load power 130. Since neither of power stage 106 or power stage 108 is currently operating, load power 130 is lower than the determined current.
Controller 102 then activates power stage 106, via control signal 120, to output the correct current. Power stage 106 converts power from power source 104 into power at 1.0 A and 3.0 V, and transmitting it to load 110 as power signal 126. Power stage 106 solely transmitting power to load 110 is represented by current function 210 and voltage function 216 of FIG. 2A. DC-DC converter 100 continues to operate in this single phase state.
For purposes of discussion, DC-DC converter 100 now desire to provide output power 1.0 A of dual phase current at a voltage of 3V. Non-limiting examples of why the current and voltage requirements may include a user input, based on time, or change in power load. For purposes of discussion, in this example embodiment let the change in current requirements of DC-DC converter 100 be due to a request from a user. The request may come due to a reduction or increase in load, change in operating environment, or based on timing procedures.
With at a new phase of current needed, controller 102 compares the current (associated with the required new phase of current) with the current state of load power 130. Controller 102 determines that transmitting power in dual phase mode is required. The ideal switching from single phase to dual phase power modes of DC-DC converter 100 will now be further discussed with additional reference to FIG. 2B.
FIG. 2B includes a graph 218 and a graph 220 of load power 130 of DC-DC converter 100, when ideally switching from a single phase to a dual phase output. Graph 218 includes a Y-axis 222, an X-axis 224, a current function 226 and a current function 228. Current function 226 includes a portion 230 and a portion 232. Current function 228 includes a portion 234 and a portion 236. Graph 220 includes a Y-axis 238, X-axis 224 and a voltage function 240.
Graph 218 represents the current of load power 130 over time in DC-DC converter 100, whereas graph 220 represents the voltage of load power 130 over time in DC-DC converter 100. Y-axis 222 represents current in Amperes, whereas Y-axis 232 represents voltage in Volts. X-axis 224 represents time in seconds.
Current function 226 corresponds to power signal 126 of power stage 106, as shown in FIG. 1. Portion 230 has a current of 1.0 A and continues up to a time t1, whereas portion 232 has a current of 0.5 A and starts after time t1. Current function 228 corresponds to power signal 128 of power stage 108, as shown in FIG. 1. Portion 234 has a current of 0.0 A and continues up to time t1, whereas portion 236 has a current of 0.5 A and starts after time t1.
In this example, power signal 128 is zero up to time t1, so power signal 126 is equal to load power 130 up to time t1. As such, in this example, power signal 126 additionally corresponds to load power 130 up to time t1. Because load power 130 is the sum of power signal 126 and power signal 128, up to time t1, load power 130 has an associated current of 1.0 A, but is solely provided from power signal 126. On the other hand, after time t1, load power 130 has an associated current that remains 1.0 A, but includes 0.5 A from power signal 126 and 0.5 A from power signal 128. In this example, as both power stage 106 and power stage 108 are providing current after time t1, DC-DC converter 100 is operating in a dual phase mode after time t1.
Similar to FIG. 2A, in FIG. 2B, current functions 226 and 228 are each illustrated as a direct current (DC) to simplify the discussion. In should be noted that each function may be additionally described with an alternating current (AC).
Voltage function 240 corresponds to a voltage associated with load power 130, as shown in FIG. 1, over time.
Returning to FIG. 1, after determining that load power 130 needs to be transmitted in dual phase mode, at time t1, controller 102 sends control signal 120 to power stage 106 and sends control signal 122 to power stage 108. Since power stage 106 is already providing power at 1.0 A and 3.0 V, its power will need to be decreased to 0.5 A and 3.0 V. Simultaneously, power stage 108 will need to be activated and then begin transmitting power to load 110 at 0.5 A and 3.0 V. The power output by power stage 106 and power stage 108 is reflected in current functions 226 and 228 of FIG. 2B. The ideal voltage output is represent by voltage function 240 of FIG. 2B.
In an ideal system, the voltage output to load 110 would remain constant, even when transitioning from a single phase current output to a two phase current output, as shown by voltage function 240 of FIG. 2B. In practice though, the voltage output to load 110 does vary, and sometimes significantly. The voltage of power signal 126 may develop transients due to nonlinearities in the power transfer function of power stage 106, e.g., voltages of impedance components that are a function of frequency. Similarly, the voltage of power signal 128 may develop transients due to nonlinearities in the power transfer function of power stage 108. Due to the nonlinearities in the system, the voltage transients cannot be predicted and must be compensated for after they occur by a feedback loop. There are even minor transients and nonlinearities in the feedback loop itself.
The realistic voltage output when switching from single phase to dual phase power modes of DC-DC converter 100 will now be further discussed with additional reference to FIG. 2C.
FIG. 2C includes graph 218 and a graph 242 of load power 130 of DC-DC converter 100, when switching from a single phase to a dual phase output. Graph 242 includes a Y-axis 244, X-axis 224 and a voltage function 248.
Voltage function 240 corresponds to a voltage of load power 130, as shown in FIG. 1, over time. Voltage function 248 includes a transient 250, which includes a voltage overshoot 252 and a voltage undershoot 254. Transient 250 represents a voltage change when switching power transfer modes at time t1.
Returning to FIG. 1, when controller 102 instructs each of power stage 106 and power stage 108 to enter the new power transfer mode, they move from a first steady state to a second steady state. When moving from a steady state there is a voltage overshoot due to the nonlinearities of the respective transfer functions of power stage 106 and power stage 108.
For example, for purposes of discussion, presume that in a single phase operation, controller 102 outputs control signal 120 to instruct power stage 106 to output 3.0 W, and outputs control signal 122 to instruct power stage 108 to output 0.0 W. Further, let power stage 106 output 3.0 W as power signal 126 as 3.0 V at 1.0 A. Then, presume that in a dual phase operation, controller 102 outputs control signal 120 to instruct power stage 106 output 1.5 W, and outputs control signal 122 to instruct power stage 108 to output 1.5 W.
Ideally, and for purposes of discussion, suppose power stage 106 should output 1.5 W as power signal 126 as 3.0 V at 0.5 A and power stage 108 should output 1.5 W as power signal 128 as 3.0 V at 0.5 A. However, presume that power stage 106 actually, yet incorrectly, outputs 3.2 V at 0.5 A, wherein the error in the voltage is due to nonlinearities in the transfer function of power stage 106. Such a voltage overshoot corresponds to voltage overshoot 252 of FIG. 2C. In other words, even though the instructions from controller 102 may be correct, the actually produced voltage, and therefore power, from each power stage may be incorrect.
If this were to happen, power signal 126 provided by power stage 106 would be 1.6 W, power signal 128 provided by power stage 108 would be 1.5 W and load power 130 would be 3.1 W. More importantly, the voltage overshoot may damage devices in load 110.
Further, voltage overshoot 252 will generate a change in load power 130, which is detected by controller 102 via line 118. Controller 102 will compare load power 130 with a reference power to determine whether the output of power stage 106 and/or the output of power stage 108 needs to be modified. In this case, as a result of voltage overshoot 252, controller may instruct power stage 106, via control signal 120, to modify its output voltage and/or may instruct power stage 108, via control signal 122, to modify its output voltage. However, the original correction may lead to voltage undershoot 254. Again, controller 102 will compare load power 130 with a reference power to determine whether the output of power stage 106 and/or the output of power stage 108 needs to be modified. In this case, as a result of voltage undershoot 254, controller may instruct power stage 106, via control signal 120, to modify its output voltage and/or may instruct power stage 108, via control signal 122, to modify its output voltage. This feedback loop continues until transient 250 attenuates to an acceptable level. Eventually, controller 102 may instruct power stage 106 and power stage 108 to output the correct power. Due to the limited bandwidth of the feedback loop between power stage 106, power stage 108, and controller 102, the current and voltage adjustment of load power 130 may take a relatively long time.
In the example of FIG. 2C, controller 102 manages to compensate for transient 254 and reach a steady state when outputting 1.0 A of current at 3.0 V at 14 ms on X-axis 246.
Now, for purposes of discussion, suppose controller 102 again requires a single phase current output.
Controller 102 compares the voltage and current associated the required single phase current output to the voltage and current of load power 130, and again determines that the voltage and current of load power 130 are not correct. Controller 102 determines that load power 130 needs to be transmitted in a single phase at 1.0 A and 3.0 V. The ideal switching from dual phase to single phase power modes of DC-DC converter 100 will now be further discussed with additional reference to FIG. 2D.
FIG. 2D includes a graph 256 and a graph 258 of load power 130 of DC-DC converter 100, when ideally switching from a dual phase to a single phase output. Graph 256 includes a Y-axis 260, an X-axis 262, a current function 264 and a current function 266. Current function 264 includes a portion 268 and a portion 270. Current function 266 includes a portion 272 and a portion 274. Graph 258 includes a Y-axis 276, X-axis 262 and a voltage function 278.
Graph 256 represents the current of load power 130 over time in DC-DC converter 100, whereas graph 258 represents the voltage of load power 130 over time in DC-DC converter 100. Y-axis 260 represents current in Amperes, whereas Y-axis 276 represents voltage in Volts. X-axis 262 represents time in seconds.
Current function 264 corresponds to power signal 126 of power stage 106, as shown in FIG. 1. Portion 268 has a current of 0.5 A and continues up to a time t2, whereas portion 270 has a current of 1.0 A and starts after time t2. Current function 266 corresponds to power signal 128 of power stage 108, as shown in FIG. 1. Portion 272 has a current of 0.5 A and continues up to time t2, whereas portion 274 has zero current after time t1.
In this example, up to time t2, load power 130 has an associated current of 1.0 A, but includes 0.5 A from power signal 126 and 0.5 A from power signal 128. As both power stage 106 and power stage 108 are providing current up to time t2, DC-DC converter 100 is operating in a dual phase mode up to time t2. On the other hand, after time t2, power signal 128 is zero, so power signal 126 is equal to load power 130 after time t2. As such, in this example, portion 270 additionally corresponds to load power 130 after time t2. Because load power 130 is the sum of power signal 126 and power signal 128, after time t2, load power 130 has an associated current of 1.0 A, but is solely provided from power signal 126.
Similar to FIGS. 2A-B, current functions 264 and 266 are each illustrated as a direct current (DC) to simplify the discussion. In should be noted that each function may be additionally described with an alternating current (AC).
Voltage function 278 corresponds to a voltage of load power 130, as shown in FIG. 1, over time.
Returning to FIG. 1, after determining that load power 130 needs to be transmitted in a single phase mode, at time t2, controller 102 sends control signal 120 to power stage 106 and sends control signal 122 to power stage 108. Since power stage 106 is providing power at 0.5 A and 3.0 V, its power will need to be increased to 1.0 A and 3.0 V. Simultaneously, power stage 108 will need to be deactivated. The power output by power stage 106 and power stage 108 is reflected in current functions 264 and 266 of FIG. 2D. The ideal voltage output is represent by voltage function 278 of FIG. 2D.
In an ideal system, the voltage output to load 110 would remain constant, even when transitioning from a dual phase current output to a single phase current output, as shown by voltage function 278 of FIG. 2D. In practice though, the voltage of power signal 126 may develop transients as discussed above.
The realistic switching from single phase to dual phase power modes of DC-DC converter 100 will now be further discussed with additional reference to FIG. 2E.
FIG. 2E includes graph 256 and a graph 280 of an output of DC-DC converter 100, when switching from a dual phase to a single phase output. Graph 280 includes a Y-axis 282, X-axis 262 and a voltage function 284.
Voltage function 284 corresponds to a voltage of load power 130, as shown in FIG. 1, over time. Voltage function 284 includes a transient 286, which includes a voltage overshoot 288 and a voltage undershoot 290. Transient 286 represents a voltage change when switching power transfer modes at time t2.
Similar to the situation discussed above with reference to FIG. 2C, here, the nonlinearities in power stage 106 and/or power stage 108 create transients in the output voltage that may be so large (in amplitude) that they risk damaging load 110.
A problem with the conventional system and method for utilizing DC-DC converters is that a transient voltage is created in the output during the transition from two different transfer modes (e.g. the transition from single phase to dual phase or dual phase to single phase operation). The error in the output voltage must be corrected for by a regulation loop. The error in the voltage output takes a relatively long time to correct due to the limited bandwidth of the regulation loop.
What is needed is a system and method for switching between two different transfer modes that minimizes transients in the output voltage of the DC-DC converter.